1. Field of Invention
This invention relates to a novel group of fluoroanilines, namely, selected 5-substituted-2-fluoroanilines and to a method for preparing these compounds by deoxygenating and hydrofluorinating a selected 3-substituted nitrobenzene.
2. Prior Art
The prior art discloses that deoxygenation and hydrofluorination of nitrobenzenes with an open para-position produces para-fluoroanilines. U.S. Pat. No. 3,558,707 discloses a process for producing such parafluorinated anilines by heating a corresponding nitrobenzene with anhydrous hydrogen fluoride and a deoxygenating agent selected from the group consisting of elemental phosphorus, elemental sulfur, phosphorus trihalides, sulfur halides in which sulfur has a valence lower than 6, aryl phosphorus halides, aryl sulphenyl halides and triaryl phosphines at a temperature of 0.degree. to 230.degree. C. under a pressure of 15-1500 p.s.i.a. U.S. Pat. No. 3,580,951 discloses a process for preparing parafluoroanilines utilizing a similar procedure wherein the reaction is conducted in an atmosphere containing a substantial portion of carbon monoxide. U.S. Pat. No. 3,639,482 discloses still another process for producing para-fluoroanilines wherein a nitrobenzene and anhydrous hydrogen fluoride are heated in an atmosphere of carbon monoxide in the presence of a noble metal catalyst. The preparation of parafluoroanilines by catalytic hydrogenation of nitrobenzene in anhydrous hydrogen fluoride is also disclosed and claimed in U.S. Pat. No. 2,884,458.
One skilled in the art would expect that reacting a 3-substituted nitrobenzene having an open para-position with anhydrous hydrogen fluoride and a deoxygenating agent would produce a corresponding parafluoroaniline. It has now been discovered, however, that when a nitrobenzene substituted in the 3 position with a hydroxyl or lower alkoxyl group is reacted at elevated temperature and pressure with anhydrous hydrogen fluoride and deoxygenating agent, that fluorine substitution occurs, in the position para to the hydroxyl or alkoxyl substituent rather than in the position para to the resulting amine group as one skilled in the art would expect.
Fluoroanilines are well-known to be useful intermediates in the preparation of dyes, herbicides and pesticides and in the preparation of various other useful compounds, and the present fluoroanilines share the wide utility of this group of compounds.
In particular, the present fluroanilines are useful in the preparation of p-fluorophenols and ester, acid and ether derivatives thereof. For example, 5-hydroxy-2-fluoroaniline is converted to 4-fluorophenoxyacetic acid or esters thereof by first reacting it by known means with NaNO.sub.2, HCl and NaBF.sub.4 to form a corresponding diazonium fluoroborate then deaminating by refluxing in the presence of zinc and ethanol. The p-fluorophenol thus formed is then refluxed with chloroacetic acid and pyridine in the presence of benzene to form 4-fluorophenoxyacetic acid which has been reported to be effective in the control of weeds. See B. R. Andersen, et al., WEEDS, Vol. 1, No. 6 (1952). Similarly p-fluorophenol is reacted with dodecyl alcohol by known means to form 4-fluorophenyldodecyl ether, reported to be an active herbicide. See S. R. McLane et al., WEEDS, Vol. II, No. 4 (1953). The present compounds are also readily converted by known means to herbicidal nitriles such as the 4-fluorophenoxyacetonitrile disclosed in the U.S. Pat. No. 3,467,692.
These compounds are also useful intermediates for preparation of dyes. For example, 5-methoxy-2-fluoroaniline is reacted at 0.degree. C. with NaNO.sub.2 and HCl to form the corresponding diazonium chloride. The diazonium chloride is then coupled at room temperature with Naphthol A.S. to form a color fast dye having an orange to red color. See Inukai, et al., J. Chem. Soc. Japan, Ind. Chem Section 58, 592 (1955).